# Please could you check this working for me?

• lioric
In summary, the pulley has a coefficient of kinetic friction of 0.25, and as block A moves up the incline, its kinetic energy decreases by 97.83 joules.
lioric
Plz could you check this working for me??

## Homework Statement

Two blocks, A and B (with mass 50 kg and 100 kg, respectively), are connected by a string, as
shown in figure.

The pulley is frictionless and of negligible mass. The coefficient of kinetic friction between
block A and the incline is μk = 0.25. Determine the change in the kinetic energy of block A as
it moves from (C) to (D), a distance of 20 m up the incline (and block B drops down a
distance of 20 m) if the system starts from rest.

Block A
T-μR+mg sinθ= ma

Block B

mg-T=ma

## The Attempt at a Solution

acceleration in both blocks is the same since they are connected directly with no elastic strings

Block A
T=ma+μR-mg sinθ

Block B
T=mg-ma

Substitute for T

mg-ma=ma+μR-mg sinθ
(100 x 9.8) - (100a) = (50a) + (0.25 x 50 x 9.8 x cos 37) - (50 x 9.8 x sin 37)
980-100a-50a=97.83-294.89
-100a-50a=97.83-294.89-980
-150a=-1177.057
a=7.8

is this correct?

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lioric said:

## Homework Statement

Two blocks, A and B (with mass 50 kg and 100 kg, respectively), are connected by a string, as
shown in figure.

The pulley is frictionless and of negligible mass. The coefficient of kinetic friction between
block A and the incline is μk = 0.25. Determine the change in the kinetic energy of block A as
it moves from (C) to (D), a distance of 20 m up the incline (and block B drops down a
distance of 20 m) if the system starts from rest.

## Homework Equations

Block A
T-μR+mg sinθ= ma
You have a signage error here...which way does the weight component act along the plane? Once you find the acceleration, then you need to find the speed of the blocks to get the KE change. Alternatively, using work-energy methods, you will get the same result.

oh i see so are you saying that it should be more like

T-μR-mg sinθ= ma

because the component of weight is opposite to tension?

lioric said:
oh i see so are you saying that it should be more like

T-μR-mg sinθ= ma

because the component of weight is opposite to tension?
Yes, that is correct, and i think the best way to proceed to then find the speed of the block A and its KE change.

Thank you very much i feel that i have learned a lot since i joined here

## 1. What does "checking the working" mean in the context of your work?

The phrase "checking the working" refers to the process of reviewing and verifying the accuracy and validity of a scientific experiment or analysis. This involves carefully examining all of the steps and calculations involved in the experiment or analysis to ensure that they are correct and free of errors.

## 2. Why is it important to have someone else check your working?

Having someone else check your working is important because it provides an extra level of validation and can help identify any potential errors or oversights that may have been missed by the original researcher. This helps to ensure the accuracy and reliability of the results.

## 3. How does the checking process differ between different fields of science?

The checking process may differ between different fields of science, but the general idea is the same. In experimental sciences, the focus may be on replicating the experiment and verifying the results. In theoretical sciences, the focus may be on reviewing the logic and assumptions behind the analysis. In all cases, the goal is to ensure the accuracy and validity of the work.

## 4. What are some common mistakes that can be caught during the checking process?

Some common mistakes that can be caught during the checking process include mathematical errors, incorrect data entry, faulty assumptions, and overlooked variables or factors. These mistakes can significantly impact the results and conclusions of a study, so it is important to catch and correct them before publishing or presenting the work.

## 5. How can I improve my own checking process?

To improve your own checking process, it is important to adopt a critical mindset and approach your work with a thorough and detail-oriented perspective. It can also be helpful to seek feedback and input from colleagues or experts in the field. Additionally, taking breaks and returning to the work with fresh eyes can help identify any potential mistakes or oversights that may have been missed initially.

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